Field of the Invention
The invention relates generally to a read head for magnetic tape, and more particularly to a tunneling magnetoresistive (TMR) type of read head with a flux guide for directing magnetic flux from the magnetic tape to the TMR sensor.
Background of the Invention
One proposed type of magnetoresistive sensor used as the read head in magnetic recording tape drives is a magnetic tunnel junction sensor, also called a tunneling MR or TMR sensor. A TMR sensor has a stack of layers that includes two ferromagnetic layers separated by a tunneling barrier layer, i.e., a nonmagnetic electrically insulating spacer layer, which is typically MgO. One ferromagnetic layer adjacent the tunneling barrier layer has its magnetization direction fixed, such as by being pinned by exchange coupling with an adjacent antiferromagnetic layer, and is referred to as the reference layer. The other ferromagnetic layer adjacent the tunneling barrier layer has its magnetization direction free to rotate in the presence of external magnetic fields from recorded data on the tape and is referred to as the free layer. With a sense current applied perpendicularly through the sensor layers, the rotation of the free-layer magnetization relative to the reference-layer magnetization due to the presence of external magnetic fields is detectable as a change in electrical resistance.
U.S. Pat. No. 8,472,148 B2, assigned to the same assignee as this application, describes a magnetic tape read head with a TMR sensor and a flux guide that directs magnetic flux from the tape-bearing surface (TBS) of the read head to the TMR sensor, which is recessed from the TBS. The flux guide is formed on an insulating layer and the flux guide and insulating layer are located between two non-magnetic electrically conducting gap layers, with the edges of the flux guide, insulating layer and gap layers being exposed at the TBS. The insulating layer electrically separates the two conductive gap layers so that all of the sense current is directed through the TMR sensor.
Magnetic tapes typically use particulate media, which is abrasive and can cause scratching of the TBS. The scratching of the edges of the gap layers and insulating layer can result in a conductive path across the insulating layer, which can cause an electrical short of the sense current.
What is needed is a tape head with a TMR sensor and flux guide that is less likely to cause an electrical short in the presence of scratches of the TBS.